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NCERT solutions Science Textbook for Class 10 chapter 12 Electricity

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Chapter 12 - Electricity

Page 200

What does an electric circuit mean?

Q 1 | Page 200 | view solution

Define the unit of current.

Q 2 | Page 200 | view solution

Calculate the number of electrons constituting one coulomb of charge.

Q 3 | Page 200 | view solution

Page 202

Name a device that helps to maintain a potential difference across a conductor.

Q 1 | Page 202 | view solution

What is meant by saying that the potential difference between two points is 1 V?

Q 2 | Page 202 | view solution

How much energy is given to each coulomb of charge passing through a 6 V battery?

Q 3 | Page 202 | view solution

Page 209

On what factors does the resistance of a conductor depend?

Q 1 | Page 209 | view solution

Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

Q 2 | Page 209 | view solution

Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

Q 3 | Page 209 | view solution

Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

Q 4 | Page 209 | view solution

Use the data in Table 12.2 to answer the following –
Table 12.2 Electrical resistivity of some substances at 20°C

Material Resistivity (Ω m)
Conductors Silver 1.60 × 10−8
Copper 1.62 × 10−8
Aluminium 2.63 × 10−8
Tungsten 5.20 × 10−8
Nickel 6.84 × 10−8
Iron 10.0 × 10−8
Chromium 12.9 × 10−8
Mercury 94.0 × 10−8
Manganese 1.84 × 10−6
Constantan
(alloy of Cu and Ni)
49 × 10−6
Alloys Manganin
(alloy of Cu, Mn and Ni)
44 × 10−6
Nichrome
(alloy of Ni, Cr, Mn and Fe)
100 × 10−6
Glass 1010 − 1014
Insulators Hard rubber 1013 − 1016
Ebonite 1015 − 1017
Diamond 1012 − 1013
Paper (dry) 1012
Q 5 | Page 209 | view solution

Page 213

Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series.

Q 1 | Page 213 | view solution

 Redraw the circuit of question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter?

Q 2 | Page 213 | view solution

Page 216

Judge the equivalent resistance when the following are connected in parallel − (a) 1 Ω and 106Ω, (b) 1 Ω and 103Ω and 106Ω.

Q 1 | Page 216 | view solution

An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 Vsource. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?

Q 2 | Page 216 | view solution

What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

Q 3 | Page 216 | view solution

How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?

Q 4 | Page 216 | view solution

What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?

Q 5 | Page 216 | view solution

Page 218

Why does the cord of an electric heater not glow while the heating element does?

Q 1 | Page 218 | view solution

Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.

Q 2 | Page 218 | view solution

An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.

Q 3 | Page 218 | view solution

Page 220

What determines the rate at which energy is delivered by a current?

Q 1 | Page 220 | view solution

An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.

Q 2 | Page 220 | view solution

Pages 221 - 222

A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is -

(a) 1/25
(b) 1/5
(c) 5
(d) 25

Q 1 | Page 221 | view solution

Which of the following terms does not represent electrical power in a circuit?
(a) I2R
(b) IR2
(c) VI
(d) V2/R

Q 2 | Page 221 | view solution

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W

Q 3 | Page 221 | view solution

Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –

(a) 1:2

(b) 2:1

(c) 1:4

(d) 4:1

Q 4 | Page 221 | view solution

How is a voltmeter connected in the circuit to measure the potential difference between two points?

Q 5 | Page 221 | view solution

A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10−8Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?

Q 6 | Page 221 | view solution

The values of current I flowing in a given resistor for the corresponding values of
potential difference V across the resistor are given below –

I (amperes) 0.5 1.0 2.0 3.0 4.0
V (volts) 1.6 3.4 6.7 10.2 13.2


Plot a graph between V and I and calculate the resistance of that resistor.

Q 7 | Page 221 | view solution

When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

Q 8 | Page 221 | view solution

A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?

Q 9 | Page 221 | view solution

 How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?

Q 10 | Page 221 | view solution

Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.

Q 11 | Page 221 | view solution

Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. Ω of 220 V line if the maximum allowable current is 5 A?

Q 12 | Page 221 | view solution

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistances, which may be used separately, in series, or in parallel. What are the currents in the three cases?

Q 13 | Page 221 | view solution

Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.

Q 14 | Page 221 | view solution

 Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

Q 16 | Page 222 | view solution

An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.

Q 17 | Page 222 | view solution

Explain Why is the tungsten used almost exclusively for filament of electric lamps?

Q 18.1 | Page 222 | view solution

Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?

Q 18.2 | Page 222 | view solution

Why is the series arrangement not used for domestic circuits?

Q 18.3 | Page 222 | view solution

How does the resistance of a wire vary with its area of cross-section?

Q 18.4 | Page 222 | view solution

Why are copper and aluminium wires usually employed for electricity transmission?

Q 18.5 | Page 222 | view solution

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